FIG. 1 shows a known direct actuated clutch system 10 for a motor vehicle including a concentric slave cylinder (CSC) 12 and a hydraulic actuator unit 14 experiences degraded performance with wear of one or more clutch discs 16 of a clutch. As clutch disc 16 wears, the travel of an actuator piston 18 and a CSC piston 20 become longer to compensate for increased clearances within the clutch. As these travels increase due to wear, the engagement and disengagement times also increase. To work with the worst case travel conditions, system 10 is designed to include large and expensive components.
In system 10, actuator piston 18 needs to retract to its zero position in order to reach a bleed refill passage 22 of a reservoir 24. Passage 22 is critical to maintain the correct fluid volume in the system due to leakage and thermal expansion of the hydraulic fluid. The actuator piston 18 is also stroked to push the CSC piston 20, which is in hydraulic communication with hydraulic actuator unit 14 via a high pressure line 26, outward toward the clutch discs 16. This distance CSC piston 20 is pushed is the engagement travel. As the clutch discs 16 wear, the engagement travel increases. As the discs 16 wear, the lift-off gap in the clutch increases.